The invention relates generally to diesel engines, and more specifically to turbocharged diesel engines.
The capability of modem engines to produce more power from a given cylinder displacement has been steadily increased due to engineering innovation and development. Modem engines utilize higher charged air pressure provided by turbochargers to generate more power than their previous generation counterparts. The amount of power obtained from a cylinder in an engine depends upon how much fuel is burned in it, and upon the amount of air available in the cylinder. Therefore, by providing more air into the cylinder the power generated is increased. Turbocharging is a technique used to increase the amount of air introduced into each cylinder, typically by a positive pressure that exceeds the then reigning pressure in the cylinder. Exhaust gas from the engine typically drives the turbocharger. This gas drives a turbine, which, in turn, drives a compressor to drive the additional air into the cylinder.
Conventional diesel engines used in vehicles, such as diesel electric locomotives are difficult to start at low ambient temperatures. In some engines, the compression ratio and cranking speed are insufficient to provide adequate in-cylinder temperature and pressure for auto ignition of the diesel fuel. One of the ways this issue has been addressed is to use auxiliary power units to circulate hot fluids through the engine for enhanced cold start capability.
Certain transients or off-design operation can lead to turbocharger surge, which is damaging to the turbo machinery and associated hardware. Locomotives currently have few or no controls or hardware to avoid such damage.
To address the surge issue, turbocharged trucks and automobiles are typically equipped with waste gate systems to limit turbocharger speed. Alternately, “safe gates” or blow off valves on the compressor discharge have been used to prevent surge. Typically, compressor surge margin can be improved through aerodynamic modifications to the compressor and diffuser, but these often result in loss of compressor efficiency.
There is a need, therefore, for an improved technique for cold-start performance of diesel engines, to prevent turbocharger surge, and to control turbocharger speed independent of engine operation. There also exists a need for a technique to increase the engine performance to address the drawbacks in heretofore known systems.